Inorganic phosphate compositions, and methods for the preparation and utilization thereof



Sept. 15, 1959 J, 5. METCALF 2,904,513

INORGANIC PHOSPHATE COMPOSITIONS, AND METHODS FOR THE PREPARATION ANDUTILIZATION THEREOF Filed April 16, 1954 1N VEN TOR.

J0: J- Mere/n1" United States Patent INORGANIG' PHOSPHATE COMPOSITIONS;AND NIETHODS! FOR THE PREPARATION AND UTI-' THEREOF- 11; Claims. (Cl;252--135)' invention ;relates: to;inorganic phosphate compositions;More;specifically,xit: relates to tripolyphospihate and pyrophosphatecompositions which; have a relatively lowrrategofi precipitation oncrystallization from aqueous. solutiom Theninvention also relates to 1methods for producing; thev aforementioned phosphate. compositions. Initsnnore; generalaspects, the invention relates to methods for:controlling; the rate of; precipitation or, crystallization;.of,-phosphates from aqueous solutions. The inventionds: particularly usefulinconnection with the manufacture of detergent;compositions byv spraydrying techll- 2.

Many detergent compositions, and; especially; those of thedry,.-granular=1type, such as those. designed for home laundryusfi.,are-made up of a multiplicity-of components. Such-componentsusuallyinclude, interalia, a so-called actiye? ingredient; such as-a sulfatedorsulfonated -alkyl atedaromatie hydrocarbon .oracondensation product ofethyleneoxide. with a, long. chain 9 alkyl alcohol, or: mercap tana-predominantproportion of a. so-called. builder, such, as-sodinmtripolyphosphate or tetrasodium pyrophosphate, and a-small. amountof acorrosioninhibitor such: as .the inorganicsilicates,.e.g., sodiummetasilicate, etc..

One of the problems in formulating a satisfactory. andcommerciallyusefuhgranular;mixtureof several dry ingredieuts. is, toobtaina satisfactory uniformity. of-distributionnfieach of theseparateingredients throughout the -.bulk ,ofthe mixture. Failure to obtain suchuniformity.wi11 increase. the probability, thatsmall, portionswithdrawn.fitom.the bulkof.themixturewillhave a compositionsubstantiallydifierentfrom the overall composition ofrtheJtotalbulk.Anotherproblem in theyformulation of; such mixturesiis; to obtain asatisfactorily uniform particlesize, distributionofthe ingredients.Failure, to

obtain thislatter unformity, will give rise to a sortof,

automaticv classification processwhereby the coarse and lineparticlesqtendto separate, fromeach other during.

the transportation,and'handling of the packaged or bulk solids.

One ofthe ways, in, which the aforementioned. difficulties are overcome,or at least minimized, is by the process. known as spray drying. Insuch, a process. a slurry. ofthe solids in water is broken up intorelatively uniformly. sizedldroplets by atomizing the slurry. Thedroplets are thenpassed into or through a heated zone wherein the wateris evaporated from each of'the drop lets, leaving; discrete dry granularparticles or. agglomerates, By proper. control of the conditions underwhich the spraydrying is carried out, it ispossible to obtain areasonably uniformdistribution of particle sizes, with each" of theindivdualjparticles containing approximately the same proportions of'thevarious components.

Oneof the-factors which is particularly important in the control ofaspray'drying process is that of the viscosity, o1: consistency, oftheslurry which is to be atomized. Ifth'e. slurryis too thick or. viscous,proper atomization thereof will be very, difiicult. In such a case the.

2,904,513 Patented 7 Sept. 15, 1952.

fluidity. of the. slurry can be increased by increasingthe amount ofwater in the slurry. However, an increase in water content isundesirable since a. larger quantity of slurry mustbe handled, and alarger quantity of water must be, evaporated, for a given output of,detergent composition. Thus, it can be seen that it is very advan:tageous to have the solid content of the slurry as high as possiblewhile still' maintaining the required degree of fluidity for adequateatomization of the slurry.

As was indicated above, sodium tripolyphosphate and/. or tetrasodiumpyrophosphate are often used as a predominant, component of granulardetergent compositionsprepared by spraying drying processes. The com-.mercial'tripolyphosphate andipyrophosphates utilized in such processesare usually in anhydrous form; When these anhydrous phosphates are putinto an aqueous slurry, there is a marked tendency for the slurry to in:crease rapidly in consistency, and even set up as a completelynon-fluid'mass. This increase inconsistency or lossyof' fluidity is atleast partially caused by thereducw tion of free water content of theslurry because of'the hydration of :the anhydrous phosphates. The lossof fluidity of the slurry may also be accentuated by the manner'in whichcrystal growth of the hydrates occurs; Because of-the foregoing adverseeffects of the anhydrous phosphates, and'in order to maintain theslurryin a satisfactorily-fluid state, it; is necessary either to increase-theWater concentration of the slurry or to find away to prevent or delaythe precipitation or crystallization of the hydrates of thesephosphates.

Accordingly, it is an'object of the present inventionto provide a-methodfor decreasing the rate of crystallization of'certain phosphates fromaqueous solutions thereofi Another object of the invention is to providea novel phos phate composition which is particularly useful in theformation'of high-fluidity slurries suitable for spray dryingoperations.Itis afurther object of the present invention to'providesuitable methodsfor makingsuch phosphate compositions. An additional-object isto-provide'a novel'method forforming slurries of phosphates which arehighly suitable for spray drying processes;- Oth'er objects will'bereadily apparent from the follow-- ingdescription.

- It has now been-found that the rate of precipitation oncrystallization from aqueous solutionof sodiumphosphates-having a molarratio of Na O/P O between about 5/3 and about 2, inclusive, can besubstantially reduced} by thepresence inthe solution of minor amounts ofline arly polymeric phosphate ions having more than three phosphorousatomsin the linear chain thereof. It has also been found that a highlysuitable phosphate composition having theproperty of reduced rate ofprecipita-- tion fromaqueous solution can be prepared by intimately:

dispersingawater-soluble linearly polymeric phosphate:

of the above-type throughout a particulate mass ofathe; It has also beenfound that such phosphate compositions are particularly useful?aforesaid sodium phosphates.

inthe preparation of detergenttslurries suitable for: spray drying toform granular detergent compositions.

Typical otthe linearly polymeric phosphates suitable;

fOruse-in the various aspects of the present invention are the-sodiumphosphate glasses, i.e., the amorphous: compositions having Na O/P Omolar ratios between 1" and 1.67. As has been pointed out in variousliterature.

references (see, for example, Van Wazer, J. R., Journal 3 The term chainlengt as applied to these straight chain polymeric phosphates, refers tothe number of phosphorus atoms in the straight chain polymer.

As is also pointed out by Van Wazer, the average chain length of themixture of polymers in a sodium phosphate glass is primarily a functionof the ratio of Na O/P O in the melt from which the glass was formed.The predominant polymer in such a mixture has a chain length equal tothe whole number most closely approaching the value of the average chainlength. The proportions of the other chain length polymers in themixture become progressively smaller as the chain length increases ordecreases from the average chain length. The average chain length of theglasses becomes increasingly greater as the ratio of Na O/P O decreasesranging from a chain length of three when the Na O/P O ratio equals 5/3to a chain length of several thousands or more as the ratio of Na O/P Oapproaches unity.

As indicated previously, the linear polymers suitable for use accordingto the present invention are those having a chain length greater than 3.As the length of the chain increases, the polymers become more effectivefor purposes of the present invention. Thus, polymers having a chainlength of 4 are more effective than those having chain lengths of lessthan 4. Likewise, polymers having a chain length of 5 are more effectivethan those having a chain length of 4, polymers having a chain length of6 are more eiiective than polymers having a chain length of 5, and soon. A preferred class of linearly polymeric phosphates are those havingan average chain length greater than about 10. While the efifectivenessincreases as the chain length increases, the rate of increase ofeffectiveness with respect to increase in chain length decreases as thechain length increases. Examples of particularly desirable linearlypolymeric phosphates are the commercially available sodium phosphateglasses having molar ratios of Na O/P O of about 1.1, about 1.4 andabout 1.55.

The foregoing description stresses the importance of sodium phosphateglasses in the practice of the present invention because such glassesare very well known and more widely available than some of the othersources of linearly polymeric phosphate ions. However, it should beunderstood that any material which can supply the polymeric phosphateion is a suitable source. Examples of other suitable materials areKurrols salt (a water-soluble, crystalline linearly polymeric potassiummetaphosphate), lithium phosphates having a molar ratio of Li O/P Obetween 1 and 5/3, linearly polymeric ammonium phosphates formed eitherby replacing alkali metal ions with ammonium ions or by reaction ofammonia and P (with or without water), and the like. Also satisfactoryare the acids corresponding to the foregoing salts. In order to affectthe rate of crystallization of the tripolyand pyrophosphates, it isnecessary that the linearly polymeric phosphate ions be in solution.Consequently, any salts which are used as a source of such ions must besoluble in the tripolyor pyrophosphate solution, at least to the extentof the minimum eflfective concentration of the ion.

As indicated above, the effectiveness of the linearly polymericphosphates increases with increasing chain length of the phosphates.When these linearly polymeric phosphates are utilized withtripolyphosphates, the effectiveness also varies somewhat with thecrystalline form of the tripolyphosphate. As is well known, sodiumtripolyphosphate exists in two difierent crystalline formsone known asthe high temperature form (or Form I), and the other known as the lowtemperature form (or Form II). A preferred embodiment of the presentinvention is the use of the above-described polymeric phosphates withsodium tripolyphosphate-II, or with mixtures of Form I and Form IIcontaining more than about 75 weight percent of the Form II material.Best results are obtained when using mixtures containing less than about4 10 percent by weight of Form 1, or even less than 5 percent by weightof Form 1.

Because of the marked change in effectiveness of the polymericphosphates with respect to both the chain length of the polymers and thecrystalline form of the phosphates to which the polymers are added, theminimum effective concentration of the polymeric phosphates will varyover a rather wide range. In general, at least about 0.01 weight percent(based upon the total dry weight of phosphates present), and preferablyat least about 0.1 weight percent, should be utilized. In extreme cases,such as when using the short chain polymers in tripolyphosphate mixturescontaining relatively large proportions of the Form I modification, asmuch as 1 percent or more of the polymeric phosphate may be required.More than 10 percent will seldom be required, and under mostcircumstances 5 percent will be more than adequate.

As indicated above, a preferred embodiment of the present invention isthe preparation of tripolyphosphate or pyrophosphate compositions intowhich the watersoluble linearly polymeric phosphates have already beenincorporated. One of the simplestways to prepare such a composition isby finely grinding or otherwise comminuting the polymeric phosphate andintimately inter mixing it with the granular or powdered sodiumtripolyphosphate or pyrophosphate. Another way to form such acomposition with the polymeric phosphate intimately and uniformlydistributed throughout the bulk of the -tripolyphosphate orpyrophosphate is to form a solution of the polymeric phosphate in avolatile solvent, such as water or an alcohol-water mixture, and then tospray the solution onto or into a bed of the other phosphate. Thesolvent is evaporated from the bed, thereby precipitating the polymericphosphate within the bed of' tripolyor pyrophosphate. It is particularlyadvantageous to maintain the temperature of bed of phosphate above theboiling point of the solvent in which the polymeric phosphate isdissolved. In this way, the solvent is evaporated very quickly uponcontact with the phosphate bed, and there is less tendency for thesolventto dissolve any of the tripolyor pyrophosphate and causeclumping, agglomer-' ating, etc.

Another way of preparing suitable phosphate compositions containingsmall amounts of linearlypolymeric phosphates is by exposing sodiumtripolyphosphate to an elevated temperature for a relatively shortperiod of time in order to fuse a small amount of the material on thesurface of the tripolyphosphate particles. The fusion'loftripolyphosphate results in the formation of solid pyrophosphate andmolten linearly polymeric phosphates having an average chain lengthsomewhat above 3. While equilibrium cooling of the fusedtripolyphosphate would result in the reconversion of the pyrophosphateand linear polymers to tripolyphosphate, a relatively rapid cooling willtrap the linearly polymeric materials in a non-equilibrium glassy state,thus giving the desired tripolyphosphate composition containing a smallamount of the linearly polymeric phosphate of chain length longer than3.

The phosphate compositions into which the linearly polymeric phosphateshave been incorporated are utilized in the preparation of crutcher mixes(or slurries) or spray drying in substantially the same general mannerthat the phosphate builders have been utilized in the past. However, ahigher concentration of solids can be utilized in slurries of thepresent phosphate compositions without increasing the viscosity of theslurry, or alternatively, the viscosity of the slurry can be markedlydecreased without decreasing the concentration of solids in the slurry.

As an alternative to incorporating the polymeric additives into theslurry as an integral component of a phosphate builder composition, theadditives can be incorporated into the aqueous slurries independentlyof; the phosphate builder addition. It added independently, however, thelinearly polymeric phpsphates should be added to the slurry prior to, orat least substantially the same time as, the phosphate builder isadded.If added much later, substantial precipitation and crystallization ofthe hydrated phosphatewill have taken place before the linearlypolymeric material has an opportunity to delay such crystallization.

The term linear, or non-cyclic, as used herein with respect to thepresent polymeric phosphates, includes branched as well as normal chainphosphate polymers, but excludes the cyclic phosphates such as thetrimetaphosphates. The ammonium polyphosphates, and especially those-inwhich oxygen atoms have been replaced by imido nitrogen atoms, areexamples of linear polyphosphates believed to have'branched chains;

Further information and detailsrelative to the prac tice of thisinvention may be gained by reference to the following examples, whichalso serve to demonstrate the marked advantages to begained by-thepractice of the invention.

Example 1 Fifty grams of'9'5 percent glycen'ne and 50 g. ofpowdered-sodium triployphosphate (2.4 weight percent STP-I, remainderSTP -II) were thoroughly intermixed in a 200 ml. tall form beaker.Twenty-five milliliters of water was then added to the mixture andvigorously stirred for about 2 minutes. The resulting mixture was thenvallowed to stand for about 30 minutes. After this time the beaker wasinverted, but the consistency of the mixture had increased to such anextent that only a few drops of liquid ran out of the beaker. 'Aparallel test carried was out in the same manner, except'that 0.5 g. ofglassy sodium polyphosphate having an average chain length of about 5.5was dissolved in the 25 ml.' of "water prior to mixing with theglycerine-sodium tripolyphosphate mixture. In this latter case,theentire slurry was readily poured from the beaker after the 30 minutesof standing;

Example 2 The procedure ofExample l was duplicated, except that variouswater-soluble linearly polymericphosphates in finely divided form werephysically admixed with the sodium tn'polyphosphate prior toincorporation into the glycerine. The results of these tests aresummarized in the following table:

Sodium phosphate glass tration,

Slurry remained in beaker-alter inversion. Very small proportion ofsolids remained after inversion. BeaIIIJer completely emptied afterinversion.

0. About f/ of solids remained in bottom'of beaker I after inversion.

About of solids remained in bottom of beaker alter inversion. Beakercompletely emptied after inversion. About of solids remained inbottom ofbeaker aiter inversion. Beaker completely emptied after inversion.

Example 3 The procedure of Example 2. was duplicated; except that thewater-soluble linearly polymeric phosphate was an ammoniumpolyphosphateof the type described by Van Waz'er in Encyclopedia of ChemicalTechnology]? vol. X,, The .lnterscience Encyclopedia, Inc. (1953), pp.4191-20.. The specific ammonium polyphosphates used were reactionproducts of ammonia, P20 and water'in the respective'mol-ar proportionsof (A) 2.02/ 1.00/ 1.29 and (B) 2.9,1/l.0O/ 0.49.' Sample A had anaverage chain length of about 12 P.-atoms and a water solubility ofabout 4 weight percent. Sample B had an average chain length of about 8P-atoms and a water solubility of about 60{weight percent. (The chainlengths were determined by'the well known end group titration method.)The results obtained by mixing various concentrations of theseammoniumpolyphosphates with so-v dium tiipolyphosphates are, summarizedin the following table:

Ammonium polyafter inversion.- 1, About V of solids remained int-bottomof beaker after inversion. I 2 Beaker completely emptied afterinversion. 2 Slurry remained in beaker after inversion.- 5 About ofsolids remaining in bottom ot-beaker inversion.

Example 5 The test Procedure of Example 2 was duplicated sl cept thatthe water-soluble linearly polymeric phosphate was formed upon thesurfaces of the sodiumtripolyphosphate particles'by briefly passing aflame over the 'surfa'ce'of' a mass of tripolyphosphate. After andallowing to stand as described in the foregoing examples, the slurryformed from the flame-treated tripolyphosphate was readily poured fromthe beaker, whereas the slurry prepared from an identicaltripolyphosphate sample without flame treatment had increased inviscosity to'such an extent that none of theslurry could be poured fromthe beaker.

Example, 6

, The procedure of Example 2 "was duplicated; except thattetra'sodiurnp'yrophosphatewas substituted for the sodiumtripolyphosphate. As inthe cases where sodium tr'ip'olyphosphate wasused, the slurry prepared"from tetrasodium pyrophosphate without anywater-soluble linearly polymeric phosphates-becamesothick that it couldnot be poured from the beaker. However, when either :5 percent ofawater-solublelinearly, polymeric-sodium phosphate havingan :average"chain length of 5.5; 0:05 weight percent of a water-solublelinearlygpolymeric sodium phosphate having an average chain length of15.5 was added to the :tetrasodium pyrophosphate, the resulting slurryretained suificient fluidity to be poured easily from the beaker..

Example 7 A solution of sodium tripolyphosphate. super-saturatedwithrespect to sodium tripolyphosphate hexahydrate was preparedbyadding-340 g. ofanhydi'ous sodium tripolyphosphate (about 2.5 weightpercent Form' I) to 1000 ml. ofwaten The mixture was stirred for tenminutes, coole'cl. to.-25 C. and filtered. To a m1; portion of thefiltrate, there were added (1) 0.6 g. of a sodium phosphate glass havinga known average chain length and (2) 10 g. of recrystallized sodiumtripolyphosphate hexahydrate. (The latter was added to provide a surfacefor crystallization of the hexahydrate from the solution.) The resultingmixture was continuously stirred while sodium tripolyphosphatehexahydrate crystallized from the solution. The rate of crystallizationwas determined by periodically withdrawing samples of the supernatantliquid and determining the dissolved solids concentration therein. Twoother 100 ml. portions of filtrate were treated in the same mannerexcept that sodium polyphosphate glasses of difierent average chainlengths were used. A fourth portion of filtrate was used as a control,being treated in the same manner as each of the others except that nopolyphosphate glass was added. The results of the :foregoing tests areset forth in the drawing in the form of a plot of the'amount of sodiumtripolyphosphate hexahydrate crystallized from the solution, as afunction of time and average chain length of the sodium polyphosphateglasses added to the solution. From this plot it can be seen that therate of crystallization from solutions of the less highly condensedphosphates, such as tetrasodium pyrophosphate and sodiumtripolyphosphate, is markedly decreased by small amounts ofwater-soluble linearly polymeric phosphates, such as the sodiumphosphate glasses.

I claim:

1. An anhydrous intimately intermixed physical admixture of anhydroussodium tripolyphosphate containing less than 10 weight percent of sodiumtripolyphosphate-I, and between about 0.01 weight percent and about 10weight percent of a water-soluble linearly polymeric phosphate salthaving a chain length greater than 3.

2. An anhydrous intimately intermixed physical admixture of anhydroussodium tripolyphosphate containing less than 10 Weight percent of sodiumtripolyphosphate-I, and between about 0.1 weight percent and about 10weight percent of a water-soluble linearly polymeric alkali metalphosphate salt having a chain length greater than 3.

3. A composition consisting essentially of anhydrous sodium phosphatesand made up of an intimately intermixed physical admixture of anhydroussodium tn'polyphosphate containing less than 10 weight percent of sodiumtripolyphosphate-I, and between about 0.1 weight percent and aboutweight percent of a mixture of watersoluble linearly polymeric sodiumphosphates having an average chain length greater than about 5.

4. A process for producing an anhydrous sodium tripolyphosphatecomposition which slowly hydrates in and crystallizes from aqueoussolutions thereof, which process comprises spraying an aqueous solutionof a watersoluble linearly polymeric phosphate salt having a chainlength greater than 3 upon a heated granular mass of anhydrous sodiumtripolyphosphate while maintaining the temperature of said granular massabove the boiling point of the solvent in said linearly polymericphosphate salt solution, the amount of said linearly polymeric phosphatesalt being between about 0.01 weight percent and about weight percent ofthe total dry weight of tripolyphosphate and linearly polymericphosphate salt.

5. A process for producing an anhydrous sodium tripolyphosphatecomposition which slowly hydrates in and crystallizes from aqueoussolutions thereof, which process comprises spraying an aqueous solutionof a mixture of water-soluble linearly polymeric sodium phosphate saltshaving an average chain length greater than about 5 upon a heatedgranular mass of anhydrous sodium tripolyphosphate while maintaining thetemperature of said mass above 100 C., the amount of said linearlypolymeric sodium phosphate salt being between about 0.01 weight percentand about 10 weight percent of the total dry weight of tripolyphosphateand linearly polymeric sodium phosphate salt.

6. In the process of utilizing anhydrous sodium tripolyphosphate inpreparing aqueous detergent slurry composition suitable for spray-dryingto a dry detergent composition containing sodium tripolyphosphate as abuilder therein the improvement which comprism separately incorporatinginto said slurry between about0.0l weight percent and about 10 Weightpercent, based upon the total phosphates in said slurry, of a mixture ofwatersoluble linearly polymeric phosphates having an average chainlength greater than 3.

7. In the process of utilizing anhydrous sodium tripolyphosphate inpreparing arr-aqueous detergent slurry composition suitable forspray-drying to a dry detergent composition containing sodiumtripolyphosphate as a builder therein, the improvement which comprisesincreasing the fiuidity of said slurry by adding said anhydrous sodiumtripolyphosphate to said slurry as an intimately intermixed physicaladmixture with between about 0.01 weight percent and about 10 Weightpercent of a mixture of water-soluble linearly polymeric sodiumphosphate salts having an average chain length greater than 3.

8. In the process of utilizing anhydrous sodium tripolyphosphate inpreparing an aqueous detergent slurry composition suitable forspray-drying to a dry detergent composition containing sodiumtripolyphosphate as a builder therein, the improvement which comprisesincreasing the fluidity of said slurry by utilizing said anhydroussodium tripolyphosphate in the form of a particulate mass having betweenabout 0.01 weight percent and about 10 weight percent of a mixture ofwatersoluble linearly polymeric phosphate salts with average chainlength greater than 3 intimately dispersed upon the surfaces of saidanhydrous sodium tripolyphosphate by precipitation from an aqueoussolution of said linearly polymeric phosphates at a temperature inexcess of C.

9. The method of retarding crystallization of hydrated sodiumtripolyphosphate from supersaturated aqueous solutions formed bydissolving anhydrous sodium tripolyphosphate in water, which methodcomprises adding to said'water prior to incorporation of said anhydroussodium tripolyphosphate a minor but effective crystallization retardingconcentration less than about 10 weight percent, based upon the totalphosphates, of a mixture of water-soluble linearly polymeric phosphateshaving chain lengths in excess of 3, the predominant water-solublelinearly polymeric phosphate salt in said mixture having a chain lengthgreater than 5.

10. The method of retarding crystallization of hydrated sodiumtripolyphosphate from supersaturated aqueous solutions formed bydissolving anhydrous sodium tripolyphosphates in water, which methodcomprises adding to said water prior to incorporation of said anhydroussodium tripolyphosphate a minor but efiective crystallization-retardingconcentration between about 0.01 weight percent and about 10 weightpercent, based upon the total phosphate, of a mixture of water-solublelinearly polymeric phosphate salts having chain lengths in excess of 3,the predominant water-soluble linearly polymeric phosplhate 6salt insaid mixture having a chain length greater t an 11. The method ofretarding crystallization of hydrated sodium tripolyphosphate fromsupersaturated aqueous solutions formed by dissolving anhydrous sodiumtripolyphosphate in water, which method comprises adding to said waterprior to incorporation of said anhydrous sodium tripolyphosphate a minorbut efiective crystallization-retarding concentration between about 0.1Weight percent and about 5 weight percent, based upon the totalphosphate, of a mixture of water-soluble linearly polymeric phosphatesalts having chain lengths in excess of 3, the predominant water-solublelinearly polymeric References Cited in the file of this patent UNITEDSTATES PATENTS Bornemann Oct. 3, 1939 Jackson Apr. 17, 1945 Beiley et alSept. 18, 1951 Hizer Dec. 16, 1952 10 OTHER REFERENCES Partridge, Hicksand Smith, A Thermal, Microscopic and X-Ray Study of the System NaPO NaP O Journal of the American Chemical Societ volume 63,

5 February 1941, pp. 454-466.

Van Wazer: Article in J.A.C.S., 1950, 72, pp. 653-655.

1. AN ANHYDROUS INTIMATELY INTERMIXED PHYSICAL ADMIXTURE OF ANHYDROUSSODIUM TRIPOLYPHOSPHATE CONTAINING LESS THAN 10 WEIGHT PERCENT OF SODIUMTRIPOLYPHOSPHATE-1, AND BETWEEN ABOUT 0.01 WEIGHT PERCENT AND ABOUT 10WEIGHT PERCENT OF A WATER-SOLUBLE LINEARLY POLYMERIC PHOSPHATE SALTHAVING A CHAIN LENGTH GREATER THAN
 3. 9. THE METHOD OF RETARDINGCRYSTALIZATION OF HYDRATED SODIUM TRIPOLYPHOSPHATE FROM SUPERSATURATEDAQUEOUS SOLUTIONS FORMED BY DISSOLVING ANHYDROUS SODIUM TRIPOLYPHOSPHATEIN WATER, WHICH METHOD COMPRISES ADDING TO SAID WATER PRIOR TOINCORPORATION OF SAID ANHYDROUS SODIUM TRIPOLYPHOSPHATE A MINOR BUTEFFECTIVE CRYSTALLIZATION RETARDING CONCENTRATION LESS THAN ABOUT 10WEIGHT PERCENT, BASED UPON THE TOTAL PHOSPHATES, OF A MIXTURE OFWATER-SOLUBLE LINEARLY POLYMERIC PHOSPHATE, OF A MIXTURE OF LENGTHS INEXCESS OF 3, THE PREDOMINANT WATER-SOLUBLE LINEARLY POLYMERIC PHOSPHATESALT IN SAID MIXTURE HAVING A CHAIN LENGTH GREATER THAN 5.